Field of the Disclosure
Aspects of the disclosure relate in general to amplifiers. Aspects include a chopper stabilized amplifier that utilizes a multi-frequency chopping signal to reduce chopping artifacts.
Description of the Related Art
Instrumentation amplifiers are used to accurately measure a variety of test and measurement signals. A medical instrumentation amplifier, for example, may be configured to measure physiological signals, such as electrocardiogram (ECG), electromyogram (EMG), electroencephalogram (EEG), pressure, impedance, and motion signals. Typically, instrumentation amplifiers are constructed as differential amplifiers exhibiting low offset, low drift, low noise, high common mode rejection, high loop gain, and high input impedance. In many cases, instrumentation amplifiers may require careful matching and trimming of circuit components to achieve a high degree of accuracy.
An instrumentation amplifier may be constructed with a discrete time switched capacitor architecture that obtains discrete signal samples. However, a discrete time architecture can produce undesirable aliasing of noise and signals, undermining the accuracy of measurement signals. Alternatively, an instrumentation amplifier may employ a chopper stabilized architecture in which a chopper circuit up-modulates a measurement signal into a higher frequency band to minimize amplifier noise and offset errors. A chopper-stabilized architecture may have a limited bandwidth, however, producing a large ripple in the passband. The ripple may make implementation of chopper-stabilized designs difficult in low power applications.
FIGS. 1-6 are graphs depicting signals for a type of chopping amplifiers of the prior art. FIG. 1 illustrates the frequency components of an input signal with a single-sided bandwidth. FIG. 2 depicts the undesirable offset and noise components of an amplifier. The frequency components include flicker noise and thermal noise. FIG. 3 illustrates the single frequency component of the modulated signal. FIG. 4 shows the double-sided bandwidth of the chopped input signal and amplifier noise. FIG. 5 illustrates chopped amplifier noise and offset. FIG. 6 illustrates a restored input signal and chopped amplifier noise.